ECE 445
Analysis and Design of Power
Electronic Circuits Lab
Old Diode and Thyristor based Experiments
– Before I joined
• Majority of the experiments
thyristor based - obsolete
• Experiments do not reflect
revised and modernized 445
curriculum
(a)
(b)
• No modern high-speed
switching circuits using
MOSFETs or IGBTs
• Full bridge thyristor circuits do
not work; half/split bridge
configuration needs to be
adopted
(c)
(d)
• Experiments are designed
with focus on motor control
• There is a setup on
cycloconverter, which is hardly
justified for basic 445 power
electronics course
• Expensive and bulky
(e)
(f)
New ECE 445 Power-Pole Board
Current
measurement
Power MOSFET
switches
Frequency
control
Logic
Supply
Input
Fuses
Fault
Protection
warning
Duty-ratio
control
External feedback
Control input
Switching
load for transients
Magnetic Boards
Transformer
Transformer
Inductor
Buck, Boost
& Buck-boost
Converter
Inductor
Flyback
Converter
Forward
Converter
Experimental Setup
500 MS/s
Oscilloscope
DC Supply
+/-12 V
Logic Supply
DC Electronic
Load
Power Pole Board
Features of the Lab. Module
• Modular laboratory setup (PEBB – Power Electronics Building
Block)
• Based on NSF initiative and multi-university collaboration
• Cost effective and requires less space
• Trial runs for ~2 semesters have yielded no safety problems so far
• Components supported by advanced SaberDesigner simulator
models, which students use for design and validation
•
•
•
•
•
•
•
Onboard PWM signal
Open loop and feedback control options
Frequency analysis
Easy setup and configuration changes
Safe banana plugs for input and output connections
Maximum input voltage : 40 V DC
Maximum operating current : 5 A DC
New G/UG National Science Foundation Proposition
Master
Controller
AC
I
n
t
e
r
m
o
d
u
l
e
C
o
m
m
u
n
i
c
a
t
i
o
n
B
u
s
a
b
c
AC-DC
DC
AC
DC
a
b
c
AC-DC
a’
b’
c’
DC-AC
AC
(a)
Power
Module 3
Power
Module 1
a’
b’
c’
DC-AC
DC
AC
(f)
a
b
c AC-DC
DC
AC
a
b
c AC-DC
DC
AC
(b)
DSP (Slave)
Controller 1
Sensor
Signals
DSP (Slave)
Controller 3
AC
byp12
byp11
o11
DC
byp13
c11
DC-AC
c12
d12
PEBB
Module
AC
DC-AC
(e)
a’
b’
DC-AC c’
(g)
AC-DC
DC
a’
DC
DC
a’
DC-AC b’
c’
a
b
c
AC
DC
DC-AC
DC-AC
b’
a
AC
b
(h)
o12
byp21
byp22
Power Device
o21
L21
L22
byp23
a21
a22
b21
Cbus
b22
c21
2
Gate drives
c22
n22
Current sensor
Sensor
Signals
o22
DSP (Slave)
Controller 2
Power
Module 2
Gate
Signals
DSP (Slave)
Controller 4
Communication
interface
Power
Module 4
From Master Controller
AC
AC
(d)
b12
Cbus
1
a
b
DC-AC c
a12
a11
Remote
Signals
AC-DC
a’
b’
c’
(c)
L11
b11
a
b
c
DC
AC
Preliminary Discrete Setup with Support from
Altera, Texas Instruments
FPGA based Motor Drive Laboratory Setup
Student Access to Modern Technology
Makes a Difference
UIC stood 1st among U.S. Universities and 3rd in world ranking in the
2005 IEEE Future Energy Challenge Competition
DSK
Fan
Transformer
Power
Stage
Display
Keypad
Filter Inductors
ECE 445 Power-Pole Board
Current
measurement
Power
switches
Frequency
control
Logic
supply
input
Fuses
Fault
protection
warning
Duty-ratio
control
External feedback
control input
Switching
load for transients
Safety Issues
• Setup is done before powering anything up
• Probe connections can be done before powering things up
• Laboratory manual clearly outlines the safety issues to the students
and safety precautions that need to be taken
• Input voltage < 40 V, maximum operating current less than 5A
• High and low-voltage logic areas are separate
•
•
•
•
• What more can we do?
Clearly tell the 445 students the nature of the experiments at the
beginning of the course. (suggestion by Univ. of Minnesota)
Take a safety test following NCF (formerly MAL) approach
Transparent enclosure
UL approved power equipments (may cost a bit more)
• Need your inputs and help
ECE 445 Power Electronics
Laboratory User Manual
Contents
1 Power-pole Board Familiarization
5
2 Buck Converter
15
3 Boost Converter
19
4 Buck-Boost Converter
23
5 Flyback Converter
27
6 Forward Converter
31
7 Switching Characteristic of MOSFET and Diode
35
8 Voltage-Mode Control
39
9 Peak Current Mode Control
45
iii
iv
SAFETY PRECAUTIONS
1
Why is safety important ?
Attention and adherence to safety considerations is even more important in a power electronics
laboratory than its required in any other undergraduate electrical engineering laboratories. Power
electronic circuits can involve voltages of several hundred volts and currents of several tens of
amperes. By comparison the voltages in all other teaching laboratories rarely exceed 20V and the
currents hardly ever exceed a few hundred milliamps.
In order to minimize the potential hazards, we will use dc power supplies that never exceed voltages
above 40-50V and will have maximum current ratings of 20A or less. Most of the time we will use dc
supplies of 20V or less and 1 A or less output current capability. However in spite of this precaution,
power electronics circuits on which the student will work may involve substantially larger voltages
(up to hundreds of volts) due to the presence of large inductances in the circuits and the rapid
switching on and off of amperes of current in the inductances. For example a boost converter can
have an output voltage that can theoretically go to infinite values if it is operating without load.
Moreover the currents in portions of some converter circuits may be many times larger than the
currents supplied by the dc supplies powering the converter circuits. A simple buck converter is an
example of a power electronics circuit in which the output current may be much larger than the dc
supply current.
2
Potential problems presented by Power Electronic circuits
• Electrical shock may take a life.
• Exploding components (especially electrolytic capacitors) and arcing circuits can cause blindness and severe burns.
• Burning components and arcing can lead to fire.
3
Safety precautions to minimize these hazards
3.1
General Precautions
• Be carm and relaxed, while working in Lab.
1
• When working with voltages over 40V or with currents over 10A, there must be at least two
people in the lab at all times.
• Keep the work area neat and clean.
• No paper lying on table or nearby circuits.
• Always wear safety glasses when working with the circuit at high power or high voltage.
• Use rubber floor mats (if available) to insulate yourself from ground, when working in the
Lab.
• Be sure about the locations of fire extinguishers and first aid kits in lab.
• A switch should be included in each supply circuit so that when opened, these switches will
de-energize the entire setup. Place these switches so that you can reach them quickly in case
of emergency, and without reaching across hot or high voltage components.
3.2
Precautions to be taken when preparing a circuit
• Use only isolated power sources (either isolated power supplies or AC power through isolation
power transformers). This helps using a grounded oscilloscope and reduces the possibility of
risk of completing a circuit through your body or destroying the test equipment.
3.3
Precautions to be taken before powering the circuit
• Check for all the connections of the circuit and scope connections before powering the circuit,
to avoid shorting or any ground looping, that may lead to electrical shocks or damage of
equipment.
• Check any connections for shorting two different voltage levels.
• Check if you have connected load at the output.
• Double check your wiring and circuit connections. It is a good idea to use a point-to-point
wiring diagram to review when making these checks.
3.4
Precautions while switching ON the circuit
• Apply low voltages or low power to check proper functionality of circuits.
• Once functionality is proven, increase voltages or power, stopping at frequent levels to check
for proper functioning of circuit or for any components is hot or for any electrical noise that
can affect the circuit’s operation.
2
3.5
Precautions while switching off or shuting down the circuit
• Reduce the voltage or power slowly till it comes to zero.
• Switch of all the power supplies and remove the power supply connections.
• Let the load be connected at the output for some time, so that it helps to discharge capacitor
or inductor if any, completely.
3.6
Precautions while modifying the circuit
• Switch Off the circuit as per the steps in section 3.5.
• Modify the connections as per your requirement.
• Again check the circuit as per steps in section 3.3, and switch ON as per steps in section 3.4.
3.7
Other Precautions
• No loose wires or metal pieces should be lying on table or near the circuit, to cause shorts
and sparking.
• Avoid using long wires, that may get in your way while making adjustments or changing
leads.
• Keep high voltage parts and connections out of the way from accidental touching and from
any contacts to test equipment or any parts, connected to other voltage levels.
• When working with inductive circuits, reduce voltages or currents to near zero before switching open the circuits.
• BE AWARE of bracelets, rings, metal watch bands, and loose necklace (if you are wearing any
of them), they conduct electricity and can cause burns. Do not wear them near an energized
circuit.
• Learn CPR and keep up to date. Your can save a life.
• When working with energized circuits (while operating switches, adjusting controls, adjusting
test equipment), use only one hand while keeping the rest of your body away from conducting
surfaces.
3
4
Experiment 1
Power-pole Board Familiarization
1.1
Introduction
The main feature of the Power-pole Board is the reconfigurable power-pole consisting of two MOSFETs and two diodes. The drive circuits for the MOSFETs are incorporated on the board, and so
are the various protection circuits for over current and over voltage. PWM signals to control the
MOSFETs can be generated onboard or supplied from an external source. The power-pole can be
configured to work in various topologies using three magnetics boards (BB board for buck, boost
and buck-boost converters, Flyback board for flyback converter, and Forward board for forward
converter) which plug into the Power-pole Board . In addition, there is an option of doing frequency analysis of each topology by injecting a small-signal sinusoidal control voltage. The board
can also be operated in voltage/current feedback mode using an external control circuit mounted
on a daughter board which plugs into the Power-pole Board board.
1.2
Board Familiarization
The basic block diagram of the Power-pole Board is shown in Fig. 1.1 and the actual board is shown
in Fig. 1.2. Please note that the location of the various components on the board are indicated in
Table 1.1.
1.2.1
Power-pole
The power-pole consists of MOSFETs Q10 and Q15 and diodes D10 and D15. The source of the
upper MOSFET and the drain of the lower MOSFET are connected to screw terminals for external
connection, and so are the anode of upper diode and the cathode of the lower diode. The voltage
5
Table 1.1: Locations of components on Power-pole Board
No.
Component
Ref. Des.
Location
Fig. 1.2
1
Terminal V1+
J1
A-1
2
Terminal V2+
J21
L-1
3
Terminal COM (input)
J2
A-4
4
Terminal COM (output)
J22
L-6
5
DIN connector for ±12 V signal supply
J90
A-5
6
Signal supply switch
S90
B-6
7
Signal supply +12 V fuse
F90
B-5
8
Signal supply −12 V fuse
F95
B-6
9
Signal supply LED
D99
B-5
10
Fault LED
D32
D-6
11
Over voltage LED
D33
D-6
12
Over current LED
D34
D-6
13
Upper MOSFET , diode and heat sink assembly
Q15, D15
C-2
14
Lower MOSFET , diode and heat sink assembly
Q10, D10
C-4
15
Screw terminal for upper MOSFET source
J13
D-3
16
Screw terminal for lower diode cathode
J11
D-4
17
Screw terminal for upper diode anode
J12
E-3
18
Screw terminal for lower MOSFET drain
J10
E-4
19
Screw terminal for Mid-point
J18
F-3
20
Magnetics Board plug-in space
J20
H-3
21
PWM Controller UC3824
U60
I-5
22
Duty ratio pot RV64
RV64
F-5
23
Switching frequency adjustment pot RV60
RV60
I-5
24
External PWM signal input terminal
J68
G-6
25
Selector Switch Bank
S30
E-5
26
Daughter board connector
J60
H-6
27
Switched load
R22
K-5
28
Resettable Fuse
F21
L-2
29
Control selection jumpers
J62, J63
J-5
30
Ramp select jumper
J61
H-5
31
Current limit jumper
J65
H-6
32
Small-signal ac analysis selection jumper
J64
G-5
33
Input current sensor (LEM)
CS1
B-1
34
Output current sensor (LEM)
CS5
K-2
6
in
Figure 1.1: Block Diagram of Power-pole Board
Table 1.2: Test Point Details and Location on Power-pole Board
No.
Test Point
Description of Test Point
Location
1
V1+
Terminal V1+
2
V2+
Terminal V2+
K-1
3
CS1
Input current
B-4
4
CS2
Upper MOSFET source current
D-2
5
CS3
Lower diode or lower MOSFET source current
D-4
6
CS4
Output Capacitor Current
K-3
7
CS5
Output current
K-4
8
CS LOAD 1
Switched Load Voltage +ve
L-5
9
CS LOAD 2
Switched Load Voltage -ve
L-5
10
PWM
PWM Signal
E-6
11
DRAIN (upper MOSFET )
Upper MOSFET drain
D-2
11
SOURCE (upper MOSFET )
Upper MOSFET source
D-2
12
DRAIN (lower MOSFET )
Lower MOSFET drain
E-4
12
SOURCE (lower MOSFET )
Lower MOSFET source
E-4
13
ANODE (upper diode)
Upper diode anode
E-2
13
CATHODE (upper diode)
Upper diode cathode
E-2
14
ANODE (lower diode)
Lower diode anode
D-4
14
CATHODE (lower diode)
Lower diode cathode
D-4
15
GATE (upper MOSFET )
Gate of upper MOSFET
C-2
16
GATE (lower MOSFET )
Gate of lower MOSFET
C-4
Fig. 1.2
7
C-1
in
Figure 1.2: Power-pole Board
8
D
E
E
F
F
G
G
H
H
I
I
J
J
K
K
L
L
1
4
5
6
4
5
6
3
C
D
3
B
C
2
A
B
2
1
A
and current waveforms at the terminals of the MOSFETs and diodes can be observed.
Note : Take care whenever you are using oscilloscope probes to measure voltage. If the measurement reference potential is different to the oscilloscope reference potential, you must use differential probe.
To observe the voltage across the upper MOSFET ,
• Connect the positive and negative terminals of a differential probe to the DRAIN and
SOURCE of upper MOSFET .
To observe the upper MOSFET source current,
• Connect the positive and negative terminals of a differential probe to terminals CS2 and
SOURCE (D-2 in Fig. 1.2) of upper MOSFET . The current sense resistor value is 0.05 Ω.
To observe the voltage across the lower MOSFET ,
• Connect an oscilloscope probe to the DRAIN and its ground to the SOURCE (E-4 in Fig.
1.2) of the lower MOSFET .
To observe the lower MOSFET source current,
• Connect an oscilloscope probe to terminal CS3 and its ground to the SOURCE (E-4 in Fig.
1.2) of the lower MOSFET . The current sense resistor value is 0.05 Ω. The same test points
also measure the lower diode current if that is included in the circuit.
To observe the voltage across the upper diode,
• Connect the positive and negative terminals of a differential probe to termianl CATH and
ANODE (E-2 in Fig. 1.2) of the upper diode.
To observe the voltage across the lower diode,
• Connect an oscilloscope probe to CATH LOW and its ground to the ANODE of the lower
diode (D-4 in Fig. 1.2).
1.2.2
Magnetics Boards
To build various converters using the Power-pole Board , three plug in boards are provided:
9
1. BB Board (Fig. 1.3(a)): For buck, boost and buck-boost converters
2. Flyback Board (Fig. 1.3(b)): For flyback converter
3. Forward Board (Fig. 1.3(c)): For forward converter
How to use these boards will be described in the subsequent experiments.
(a) BB Board
(b) Flyback Board
(c) Forward Board
Figure 1.3: Magnetics Boards
1.2.3
Signal Supply
±12 volts signal supply is required for the MOSFET drive circuits and also the measurement and
protection circuits. This is obtained from a wall-mounted isolated power supply, which plugs into
the DIN connector J90 (A-5 in Fig. 1.2). Switch S90 (B-6 in Fig. 1.2) controls the signal power
to the board. Each time a fault occurs, turn off and turn on this switch to reset the board. The
green LED D99 (B-5 in Fig. 1.2) indicates if the +12 V signal supply is available to the board.
Fuses F90 (B-5 in Fig. 1.2) and F95 (B-6 in Fig. 1.2) provide protection for the +12 V and −12 V
supplies respectively.
1.2.4
Load
Any external load is to be connected across terminals V2+ and COM (L-1 and L-6 in Fig. 1.2).
An onboard switched load is provided to facilitate the observation of the transient response of any
converter built using the power-pole . Thus it is possible to periodically switch in and out a 20 Ω
load (K-4 to K-6 in Fig. 1.2). The frequency and duty ratio of this load is fixed at 10 Hz and 10%.
To select the switched load,
10
• Put switch 3 of selector switch bank S30 (E-5 in Fig. 1.2) to the top position (Load(SW)
ON).
In order to observe the switched load current,
• Connect the positive and negative terminals of a differential probe to CS LOAD 1 and
CS LOAD 2 (L-5 in Fig. 1.2). This measures the voltage across the 20 Ω resistor.
• Switched load current is the measured voltage divided by 20.
1.2.5
Input/Output Voltage Measurement
Test points for input/output voltage measurements are provided on the Power-pole Board .
For input voltage measurement,
• Connect the oscilloscope probe to test point V1+ (C-1 in Fig. 1.2) and its ground to COM
(D-1 in Fig. 1.2).
For output voltage measurement,
• Connect the oscilloscope probe to test point V2+ (K-1 in Fig. 1.2) and its ground to COM
(L-1 in Fig. 1.2).
1.2.6
Current Measurement
LEM current sensors (B-1, K-2 in Fig. 1.2) are provided to measure the input and output currents.
The input current sensor is located after the input filter capacitor, and the output current sensor
is located before the output filter capacitor. Calibration of the current sensors is such that for 1A
current flowing through each, the output is 0.5 V. These signals are amplified by a factor of 2 and
are brought out to the daughter board connector J60, for use in feedback current control. Currents
through the MOSFETs and output capacitor are measured using current sense resistors. Refer to
Table 1.2 for details of the various current measurement test points.
To measure input current,
• Connect oscilloscope probe to CS1 (B-1 in Fig. 1.2) and its ground to COM (D-1 in Fig.
1.2).
To measure output current,
11
• Connect oscilloscope probe to CS5 (K-2 in Fig. 1.2) and its ground to COM (L-1 in Fig.
1.2) .
To measure output capacitor ripple current,
• Connect oscilloscope probe to CS4 (K-3 in Fig. 1.2) and its ground to COM. The current
sense resistor value is 0.1 Ω.
1.2.7
MOSFET Drive Circuit
The power-pole MOSFETs are driven by high side drivers IR2127. These drivers have in-built
overcurrent protection using a current-sense resistor for each MOSFET (see locations C-3 and C-5
in Fig. 1.2). The voltage across these sense resistors can be observed using test points provided on
the board.
To see the upper MOSFET current,
• Connect the positive and negative terminals of a differential probe to CS2 and SOURCE
of upper MOSFET .
To see the lower MOSFET current,
• Connect an oscilloscope probe to CS3 and its ground to SOURCE of lower MOSFET .
Note: The lower diode current can also be observed using test point CS3. However the upper diode
current cannot be observed.
1.2.8
PWM Signal Generation
PWM signals required for the MOSFETs can be generated using the on-board PWM controller
UC3824 (I-5 in Fig. 1.2). There is also an option to supply PWM signals from an external source.
To use the onboard PWM,
• Put switch 2 of the selector switch bank S30 (E-5 in Fig. 1.2) to its bottom position (PWM
INT.).
To use external PWM,
• Put switch 2 of the selector switch bank S30 to its top position (PWM EXT.).
12
• Connect the external PWM signal to the terminal J68 (G-6 in Fig. 1.2).
While using the onboard PWM for operation of the power-pole in open-loop, the duty ratio can be
controlled using pot RV64 (F-5 in Fig. 1.2). The duty ratio can be varied from 4% to 98%. The
frequency of the PWM can be adjusted using the trim pot RV60 (I-5 in Fig. 1.2).
There is a provision for providing an external ramp to the UC3824 IC. This is useful for peak
current mode control. For this, remove jumper J61 (H-5 in Fig. 1.2) and use the RAMP pin on
daughter board connector J60.
1.2.9
Frequency Analysis
Frequency analysis of any converter built using the power-pole can be done by injecting a low
voltage sinusoidal signal at jumper J64 (G-5 in Fig. 1.2). To do this,
• Remove jumper J64.
• Connect the small signal sinusoidal source at the jumper terminal J64.
Note: J64 is to be shorted in all other modes of operation.
1.2.10
Power-pole Board in Feedback Control Mode
The power-pole board can be operated in either open or closed loop and is selected by jumpers J62
and J63 (J-5 in Fig. 1.2). For open loop operation,
• Keep J62 and J63 in the righthand positions.
Closed loop operation will be described in the relevant experiment.
13
14
Experiment 2
Buck Converter
2.1
Objective
The objective of this experiment is to study the characteristics of a simple buck converter. The
circuit will be operated under continuous current mode (CCM) and open loop conditions (no
feedback). Our main goal will be to compare the theoretical results with the experimental results .
LEM
LEM
V1+
DRIVE
CIRCUIT
V2+
V2+
V1+
Variable
Power
Resistor
Vd
MID POINT
INDUCTOR BOARD
COM
COM
COM
SWITCHED LOAD
DRIVE
CIRCUIT
DIN
ON
PWM TO TOP
MOSFET
USE EXTERNAL
PWM SIGNAL
SWITCHED
LOAD ACTIVE
PWM TO BOT.
MOSFET
USE ONBOARD
PWM SIGNAL
SWITCHED
LOAD OFF
MAGNETICS BOARD
10 Hz
10 % DUTY
DRIVE
SWITCHING
FREQUENCY
ADJUSTMENT
POTENTIOMETER
UNUSED
PWM IC
CONTROL
SELECTION
+12V
0%
100%
-12V
OFF
EXTERNAL
PWM INPUT
DUTY CYCLE
POTENTIOMETER
Figure 2.1: Schematic of Buck Converter
15
EXTERNAL
CONTROL
OPEN
LOOP
2.2
Preparing the Setup
Make the connections on the power-pole board as shown in Fig. 2.1 to use the upper MOSFET
and the lower diode.
• Use the magnetics board BB board for the buck converter circuit. The inductor is 100 µH.
• Use a variable load resistor (RL ) as a load.
• Use onboard PWM signals.
• Connect the ±12 signal supply at the DIN connector. Signal supply switch S90 should be
OFF.
2.3
Checks before powering the circuit
• Check the circuit connections as per the schematics.
• Have your circuit checked by your Lab Instructor.
2.4
Powering the Circuit
• Switch ON the signal supply. Check for green LED.
• Adjust the duty ratio to 50%.
• Adjust the switching frequency to 100kHz.
• Apply input voltage Vd of 15 volts at terminals V 1+ and COM.
2.5
Measurement and Waveforms
Take the following measurements,
2.5.1
Varying Duty Ratio
• Set the duty ratio at 50%, switching frequency at 100kHz and RL = 10Ω.
• Vary the duty ratio from 10 % to 90 % (in steps of 10%).
• Measure the average output voltage for the corresponding duty ratio.
16
• Calculate the theoretical average output voltage for the corresponding duty ratios.
• Observe and make a copy of the output ripple voltage, inductor current and capacitor current
waveforms.
2.5.2
Varying Switching Frequency
• Set the duty ratio to 50 %.
• Measure the peak-peak output ripple voltage.
• Observe and make a copy of the inductor current (CS5 ) and capacitor current (CS4 ) waveforms.
• Repeat the above procedure for different switching frequencies (40kHz, 60kHz, 80kHz).
Make sure that output voltage (V2+) is maintained at 7.5V .
2.5.3
Varying Load
• Set the switching frequency at 100kHz and duty ratio at 50%.
• Set the load resistance RL = 10 Ω.
• Add some extra load and observe and make a copy of the inductor current waveform.
• Keep increasing the load, until the buck converter enters discontinuous current mode operation. Note down the average inductor current value when the converter starts entering
discontinuous current mode of operation.
• Observe and make a copy of the output voltage, voltage across the MOSFET and diode.
2.5.4
Determining Efficiency
Determine the efficiency of the buck converter at frequencies of 40kHz, 60kHz, 80kHz and 100kHz.
• Set duty ratio at 50%.
• Set load resistance RL = 10 Ω.
• Measure the average output current Io .
• Measure the average input current Ii .
• Measure the average output voltage V2+.
17
• Measure the average input voltage Vd .
• Calculate the efficiency of the buck converter for different frequencies using the above measurements.
2.6
Lab Report
The lab report should have a brief abstract detailing what has been done in the experiment. The
remaining part of the report should consist of the information asked below along with any discussion
you feel is necessary.
• Attach a graph of duty ratio versus output voltage (V2+) using data obtained in section 2.5.1.
Also plot the theoretically calculated results on the same graph. Compare the two plots and
comment about how the buck converter works as a variable dc step down transformer.
• Plot the peak-peak ripple in the output voltage versus switching frequency using data obtained
in section 2.5.2. Plot the theoretical results on the same graph. Compare the two plots.
Comment on why you were asked to maintain the average output voltage constant.
• Attach a copy of the inductor current (CS5 ) and capacitor current (CS4 ) waveforms obtained
in section 2.5.2. Explain the relation between the two currents.
• Attach a copy of the output voltage and inductor current waveforms obtained in section 2.5.3.
Compare with the theoretically estimated waveforms.
• Plot efficiency versus frequency using the data obtained in section 2.5.4. Comment on the
results you obtain.
18
Experiment 3
Boost Converter
3.1
Objective
The objective of this experiment is to study the characteristics of a simple boost converter. The
circuit will be operated under CCM and openloop condition. Our main goal is to compare the
theoretical results with the experimental results.
Note : It is important that care is taken while doing the boost converter experiment
using the power-pole board. The input and output terminals in the case of the boost
converter are interchanged as compared to that of the buck converter. V2+ & COM
is the input and V1+ & COM is the output.
3.2
Preparing the Setup
Make the connections of the power-pole board as shown in Fig. 3.1 to use the lower MOSFET amd
the upper diode.
• Use the BB magnetics board for the boost circuit. The inductor is 100 µH.
• Use a variable load resistor as a load.
• Connect the ±12 signal supply to the DIN connector. Signal supply switch S90 should be
OFF.
3.3
Checks before powering the circuit
• Check the circuit connections as per the schematics.
19
LEM
LEM
V1+
DRIVE
CIRCUIT
V2+
Variable
Power
Resistor
V2+
V1+
Vd
MID POINT
INDUCTOR BOARD
COM
COM
COM
SWITCHED LOAD
DRIVE
CIRCUIT
DIN
PWM TO TOP
MOSFET
ON
USE EXTERNAL
PWM SIGNAL
SWITCHED
LOAD ACTIVE
MAGNETICS BOARD
10 Hz
10 % DUTY
DRIVE
SWITCHING
FREQUENCY
ADJUSTMENT
POTENTIOMETER
UNUSED
+12V
0%
100%
-12V
OFF
PWM TO BOT.
MOSFET
USE ONBOARD
PWM SIGNAL
EXTERNAL
PWM INPUT
EXTERNAL
CONTROL
PWM IC
CONTROL
SELECTION
OPEN
LOOP
DUTY CYCLE
POTENTIOMETER
SWITCHED
LOAD OFF
Figure 3.1: Schematic of Boost Converter
• Confirm that you have connected the input and output terminals correctly to source and load
as shown in Fig. 3.1.
• Have your circuit checked by your Lab Instructor.
3.4
Powering the Circuit
• Switch ON the signal supply. Check for green LED.
• Set the duty ratio to its minimum.
• Set RL = 50Ω.
• Adjust the switching frequency to 100kHz.
• Apply input voltage Vd of 10 volts at terminals V 2+ and COM .
3.5
Measurements
Take the following measurements,
3.5.1
Varying Duty Ratio
• Vary the duty ratio from minimum to 70% (in steps of 10%).
20
• Measure the average DC load voltage(V1+) for the corresponding values of duty ratio .
• Calculate the theoretical average output voltage for the corresponding duty ratios.
• Compare the observed average output voltage results with the calculated ones.
3.5.2
Varying Switching Frequency
• Set the duty ratio to 50%, switching frequency to 100kHz, RL = 50Ω.
• Observe and make a copy of the input current (CS5 ) ripple waveform.
• Observe and make a copy of the output voltage (V1+) ripple waveform.
• Calculate the peak-peak input current ripple.
• Repeat the above procedure for different switching frequencies (say 40kHz, 60kHz, 80kHz).
3.5.3
Varying Load
• Set the duty ratio to 35%, RL = 50Ω and switching frequency to 100kHz.
• Keep increasing the load until the converter enters into the discontinuous conduction mode.
• Observe and make a copy of the input current to identify that the boost converter has gone
into discontinuous conduction mode.
• Observe and make a copy of the voltage across MOSFET , voltage waveform across diode
(Use differential probe).
3.5.4
Determining Efficiency
• Set the duty ratio to 50%.
• Adjust the load resistance so that load current is 0.4A.
• Measure the efficiency at switching frequencies of 40kHz, 60kHz, 80kHz, 100kHz.
3.6
Lab Report
The lab report should have a brief abstract detailing what has been done in the experiment. The
remaining part of the report should consist of the information asked below along with any discussion
you feel is necessary.
21
• Attach a graph of duty ratio versus output voltage using the data obtained in section 3.5.1.
Also plot the theoretically calculated results on the same graph. Compare the two plots.
Comment about how the boost converter works as a variable dc step-up transformer.
• Plot the peak-peak ripple in the output voltage versus switching frequency using the data
obtained in section 3.5.2. Plot the theoretical results on the same graph. Compare the two
graphs and comment.
• Attach a copy of the inductor current (CS5 ) waveform obtained in section 3.5.2. Plot the
experimental and theoretically estimated input ripple current on the same graph. Compare
the two graphs and comment.
• Plot efficiency versus frequency using the data obtained in section 3.5.4. Comment on the
results you obtain.
• Compare and comment on the efficiencies of the buck converter (obtained in Experiment 2)
and the boost converter.
22
Experiment 4
Buck-Boost Converter
4.1
Objective
The objective of the experiment is to study the characteristics of the simple buck-boost converter.
The circuit will be operated under CCM and openloop conditions. Our main goal is to compare
the theoretical results with the experimental results.
Note : It is important that care is taken while doing the buck-boost converter experiment using the power-pole board. The input and output terminals in the case
of the buck-boost converter are different as compared to that of the buck or boost
converters.
4.2
Preparing the Setup
Make the connections for the power-pole board as shown in Fig. 4.1
• Use the BB magnetics board for the buck-boost converter circuit. The inductor value is
100 µH.
• Use a variable load resistor as a load.
• Connect the ±12 signal supply to the DIN connector. Signal supply switch S90 should be
OFF.
4.3
Checks before powering the circuit
• Check the circuit connections as shown in Fig. 4.1.
23
LEM
LEM
V1+
DRIVE
CIRCUIT
Vd
V2+
V1+
V2+
MID POINT
Variable
Power
Resistor
COM
INDUCTOR BOARD
COM
COM
SWITCHED LOAD
DRIVE
CIRCUIT
DIN
ON
PWM TO TOP
MOSFET
USE EXTERNAL
PWM SIGNAL
SWITCHED
LOAD ACTIVE
PWM TO BOT.
MOSFET
USE ONBOARD
PWM SIGNAL
SWITCHED
LOAD OFF
MAGNETICS BOARD
10 Hz
10 % DUTY
DRIVE
SWITCHING
FREQUENCY
ADJUSTMENT
POTENTIOMETER
UNUSED
PWM IC
CONTROL
SELECTION
+12V
0%
100%
-12V
OFF
EXTERNAL
PWM INPUT
EXTERNAL
CONTROL
OPEN
LOOP
DUTY CYCLE
POTENTIOMETER
Figure 4.1: Schematic of Buck-Boost Converter
• Confirm that you have connected the input and output terminals correctly to source and load
as shown in Fig. 4.1.
• Have your circuit checked by your Lab Instructor.
4.4
Powering the Circuit
• Switch ON the signal supply. Check for green LED.
• Set the duty ratio to its minimum.
• Set RL = 50Ω.
• Adjust the switching frequency to 100kHz.
• Apply input voltage Vd of 10 volts at the terminals V 1+ and V 2+.
4.5
Measurements
Take the following measurements,
4.5.1
Varying Duty Ratio
• Vary the duty ratio from minimum to 70% (in steps of 10%).
24
• Measure the average DC load voltage (V2+) for the corresponding values of duty ratio.
• Calculate the average theoretical DC output voltage for the corresponding duty ratios.
• Compare the observed average output voltage results with the calculated ones.
4.5.2
Varying Switching Frequency
• Set the duty ratio to 50%, switching frequency to 100kHz, RL = 50Ω.
• Observe and make the copy of the inductor current (CS5 ) ripple waveform.
• Observe and make the copy of the output voltage (V2+) ripple waveform.
• Calculate the peak-peak inductor current ripple.
• Repeat the above procedure for different switching frequencies (say 40kHz, 60kHz, 80kHz).
4.5.3
Varying Load
• Set the duty ratio to 50%, RL = 50Ω and switching frequency to 100kHz.
• Keep increasing the load until the converter enters into the discontinuous conduction mode.
• Observe and make a copy of the inductor current (CS5 )to identify that the buck-boost converter has gone into discontinuous conduction mode.
• Observe and make a copy of the voltage across MOSFET (Use differential probe), voltage
waveform across diode.
4.5.4
Determining Efficiency
• Set the duty ratio to 50%.
• Adjust the load resistance so that load current is 0.25A.
• Measure the efficiency at switching frequencies of 40kHz, 60kHz, 80kHz, 100kHz.
4.6
Lab Report
The lab report should have a brief abstract detailing what has been done in the experiment. The
remaining part of the report should consist of the information asked below along with any discussion
you feel is necessary.
25
• Attach a graph of duty ratio versus output voltage (CS5 ) using the data obtained in section
4.5.1. Also plot the theoretically calculated results on the same graph. Compare the two
plots. Comment about how the buck-boost converter works as a variable dc step-down or
step-up transformer.
• Attach a copy of the inductor current (CS5 ) waveform obtained in section 4.5.2. Plot the experimental and theoretically estimated ripple current waveforms on the same graph. Compare
the two graphs and comment.
• Plot the efficiency versus frequency using the data obtained in section 4.5.4. Comment on
the results you obtain.
• Compare and comment on the efficiencies obtained in the buck, boost and buck-boost converters.
26
Experiment 5
Flyback Converter
5.1
Objective
The objective of this experiment is to study the characteristics of the flyback converter using the
power-pole board in open loop control mode. Our main goal is to compare the theoretical results
with the experimental results.
5.2
Preparing the Setup
Make the connections on the power-pole board as shown in Fig. 5.1 to use the lower MOSFET.
• Use the Flyback magnetics board. The turns ratio is 1:1
• Use a variable load resistor as a load.
• Connect the ±12V signal supply to the DIN connector. Signal supply switch S90 should be
OFF.
5.3
Checks before Powering the Circuit
• Check the circuit connections as per the schematic.
• Check that the lower MOSFET has been selected.
• Have your circuit checked by your Lab Instructor
27
LEM
LEM
V1+
DRIVE
CIRCUIT
V2+
V2+
V1+
Variable
Power
Resistor
Vd
MID POINT
FLYBACK
COUPLED INDUCTOR
BOARD
COM
COM
COM
SWITCHED LOAD
DRIVE
CIRCUIT
DIN
ON
PWM TO TOP
MOSFET
USE EXTERNAL
PWM SIGNAL
SWITCHED
LOAD ACTIVE
PWM TO BOT.
MOSFET
USE ONBOARD
PWM SIGNAL
SWITCHED
LOAD OFF
MAGNETICS BOARD
10 Hz
10 % DUTY
DRIVE
SWITCHING
FREQUENCY
ADJUSTMENT
POTENTIOMETER
UNUSED
PWM IC
CONTROL
SELECTION
+12V
0%
100%
-12V
OFF
EXTERNAL
PWM INPUT
EXTERNAL
CONTROL
OPEN
LOOP
DUTY CYCLE
POTENTIOMETER
Figure 5.1: Schematic of Flyback Converter
5.4
Powering the Circuit
• Switch ON the signal supply. Check for green LED.
• Set the switching frequency to 100kHz and the duty ratio to 50%.
• Set RL = 30Ω.
• Apply input voltage Vd of 15V at terminal V 1+ and COM .
5.5
Measurements
Take the following measurement,
5.5.1
Varying Duty Ratio
• Vary the duty ratio from 0% to 60% (in steps of 10%).
• Measure the average output voltage (V2+) for the corresponding values of duty ratios.
• Calculate the theoretical average output voltage value for the corresponding duty ratios.
• Compare the observed average output voltage results with the calculated ones.
28
5.5.2
Constant Duty Ratio
• Set the duty ratio to 50%, switching frequency to 100kHz.
• Using differential probe, observe and make a copy of the voltage across the primary side of
the coupling inductor.
• Observe and make the copy of the voltage across the secondary side of the coupling inductor.
• Observe and make the copy of the input current (CS1 )and output current (CS5 ).
5.5.3
Switched Load Active
• Set the duty ratio to 50%.
• Set the switching frequency to 100kHz.
• Switch ON the switched load to the active position, using the selector switch bank as shown
in Fig.5.2.
• Observe and make a copy of the output voltage (V2+) waveform. Adjust the time base to
show the details of switching transients as the load is switched.
Figure 5.2: Switch Positions for Flyback Converter controller with switched load
5.5.4
Determining Efficiency
• Switch the switched load OFF.
• Keep the duty ratio constant at 50%.
• Adjust the load resistance so that load current is A.
• Measure the efficiency at the switching frequencies of 40kHz, 60kHz, 80kHz, 100kHz.
29
5.6
Lab Report
The lab report should have a brief abstract detailing what has been done in the experiment. The
remaining part of the report should consist of the information asked below along with any discussion
you feel is necessary.
• Attach a graph of duty ratio versus output voltage (V2+) using data obtained in section
5.5.1. Also plot the theoretically calculated results on the same graph. Compare the two
plots and comment about how the flyback converter works as either a step-down or step-up
transformer.
• Using the waveforms obtained in section 5.5.2, explain the relationship between the primary
and secondary voltages of the coupled inductor.
• Using the current waveforms obtained in section 5.5.2, estimate the magnetizing current
for the coupled inductor. Compare the output inductor current (CS5 ) waveforms with the
output current waveform for the buck converter obtained in ”BUCK CONVERTER EXPERIMENT”. What’s the effect of this current on the output voltage ripple.
• Using the waveforms obtained in section 5.5.3, comment on the output voltage variation due
to the effect of the switched load. What could be done to overcome this problem ?
• Plot the efficiency versus frequency using the data obtained in section 5.5.4. Comment on
the results you obtain.
30
Experiment 6
Forward Converter
6.1
Objective
The objective of this experiment is to study the characteristics of the forward converter. The
forward converter will be operated in open loop mode (no feedback). Our main goal is to compare
the theoretical results with the experimental results.
6.2
Preparing the Setup
Make the connections on the power-pole board as shown in Fig. 6.1 to use the lower MOSFET.
• Use the Forward magnetics board.
• Use a variable load resistor as a load.
• Connect the ±12V signal supply to the DIN connector. Signal supply switch S90 should be
OFF.
6.3
Checks before powering the circuit
• Check the circuit connections as per Fig. 6.1
• Confirm that you have selected the lower MOSFET.
• Have your circuit checked by your Lab Instructor
31
D1
LEM
LEM
V1+
DRIVE
CIRCUIT
V2+
V2+
V1+
Vd
Variable
Power
Resistor
D3
MID POINT
COM
D2
COM
TRANSFORMER
BOARD
COM
SWITCHED LOAD
DRIVE
CIRCUIT
DIN
ON
PWM TO TOP
MOSFET
USE EXTERNAL
PWM SIGNAL
SWITCHED
LOAD ACTIVE
PWM TO BOT.
MOSFET
USE ONBOARD
PWM SIGNAL
SWITCHED
LOAD OFF
MAGNETICS BOARD
10 Hz
10 % DUTY
DRIVE
SWITCHING
FREQUENCY
ADJUSTMENT
POTENTIOMETER
UNUSED
PWM IC
CONTROL
SELECTION
+12V
0%
-12V
OFF
100%
EXTERNAL
PWM INPUT
EXTERNAL
CONTROL
OPEN
LOOP
DUTY CYCLE
POTENTIOMETER
Figure 6.1: Schematic of Forward Converter
6.4
Power Circuit
• Switch ON the signal supply. Check for green LED.
• Set the switching to 100kHz.
• Set the duty ratio to its minimum.
• Set RL = 10Ω.
• Apply input voltage Vd of 15 V at the terminals V 1+ and COM .
6.5
Measurements
Take following measurements,
6.5.1
Varying Duty Ratio
• Vary duty ratio from minimum to 40% (in steps of 10%).
• Measure the average output voltage (V2+) for the corresponding values of duty ratio.
• Calculate the theoretical average output voltage for the corresponding duty ratios.
• Compare the observed average output voltage results with the calculated ones.
32
6.5.2
Constant Duty Ratio
• Set the duty ratio to 40%, switching frequency to 100kHz, RL = 10Ω
• Observe and make a copy of the primary side voltage of the transformer. Use a differential
probe to measure the voltage. Store the waveforms.
• Observe and make a copy of the input current (CS1 ), output current (CS5 ) and MOSFET
current (CS3 ).
6.5.3
Switched Load Active
Figure 6.2: Switch Position for Forward Converter using Switched Load
• Set the duty ratio to 40%.
• Set the switching frequency to 100kHz.
• Switch ON the switched load to the active position using the selector switch bank as shown
in Fig. 6.2.
• Observe and make a copy of the output voltage (V2+) waveform. Adjust the timebase to
show the details of the switching transients as the load is switched.
6.5.4
Determining Efficiency
• Switch the switched load OFF.
• Set the duty ratio to 40%.
• Measure the efficiency at switching frequency say 40kHz, 60kHz, 80kHz, 100kHz.
33
6.6
Lab Report
The lab report should have a brief abstract detailing what has been done in the experiment. The
remaining part of the report should consist of the information asked below along with any discussion
you feel.
• Attach a graph of duty ratio versus output voltage (V2+) using data obtained in section
6.5.1. Also plot the theoretically estimated results on the same graph. Compare the two
plots. Comment about how the converter works as a variable dc step-down transformer.
• Using the waveforms obtained in section 6.5.2, explain the detailed per switching cycle relationship between the waveforms. Explain why you have been asked to restrict the duty ratio
to a maximum of 40%.
• Using the waveforms obtained in section 6.5.2, plot the primary and tertiary winding currents
in transformer. What is the effect of the inductor on the magnetics board? Also explain the
importance of having D3 on the magnetics board?
• Comment on the output voltage variation obtained in section 6.5.3 when there is a sudden
load change.
• Plot the efficiency versus frequency using the data obtained in section 6.5.4. Comment on
the results you obtain.
34
Experiment 7
Switching Characteristic of MOSFET
and Diode
7.1
Objective
The objective of this experiment is to study the switching characteristics of power MOSFETs and
power diodes using a buck converter. The circuit will be operated in open loop conditions (no
feedback). Our main goal is to understand the switching behavior of these two power devices.
LEM
LEM
V1+
DRIVE
CIRCUIT
V2+
V2+
V1+
Variable
Power
Resistor
Vd
MID POINT
INDUCTOR BOARD
COM
COM
COM
SWITCHED LOAD
DRIVE
CIRCUIT
DIN
ON
PWM TO TOP
MOSFET
USE EXTERNAL
PWM SIGNAL
SWITCHED
LOAD ACTIVE
PWM TO BOT.
MOSFET
USE ONBOARD
PWM SIGNAL
SWITCHED
LOAD OFF
MAGNETICS BOARD
10 Hz
10 % DUTY
DRIVE
SWITCHING
FREQUENCY
ADJUSTMENT
POTENTIOMETER
UNUSED
PWM IC
CONTROL
SELECTION
+12V
0%
100%
-12V
OFF
EXTERNAL
PWM INPUT
DUTY CYCLE
POTENTIOMETER
Figure 7.1: Schematic of Buck Converter
35
EXTERNAL
CONTROL
OPEN
LOOP
7.2
Preparing the Setup
Construct the buck converter circuit as shown in Fig. 7.1 to use the upper MOSFET and lower
diode.
• Use the BB magnetics board board. The inductor is 100 µH.
• Use a variable load resistor as a load.
• Connect ±12V the signal supply to the DIN connector. Signal supply switch S90 should be
OFF.
7.3
Checks Before Powering The Circuit
• Check the circuit connections as per the schematic.
• have your circuit checked by your Lab Instructor
7.4
Powering the Circuit
• Switch ON the signal supply. Check for green LED.
• Adjust the duty ratio to 50%.
• Set the switching frequencyof 100kHz.
• Set RL = 50Ω.
• Apply input voltage Vd of 15 volts.
7.5
Measurement and Waveforms
1. Observe and make a copy of the Drain-Source voltage (VDS ) using differential probe, PWM
signal and Anode-Cathode voltage (VAK ) of lower diode.
2. Observe and make a copy of the current through the upper MOSFET (between CS2 and
Source) using a differential probe, inductor current (between CS5 and COM ), lower diode
current (between CS3 and COM ).
3. Observe and make a copy of the Anode-Cathode diode voltage VAK and diode current. Adjust
the time base to show the switching details during turn-ON and turn-OFF.
36
4. Observe and make a copy of the Drian-Source MOSFET voltage VDS and MOSFET current.
Adjust the time base to show the switching details during turn-ON and turn-OFF.
7.6
Lab Report
The lab report should have a brief abstract detailing what has been done in the experiment. The
remaining part of the report should consist of the information asked below along with any discussion
you feel necessary.
• Compare the switching waveform results obtained in step 1 of section 7.5 to the ideal voltage
waveform.
• Compare the switching current waveforms obtained using step 2 of section 7.5 to the ideal
current waveform.
• Using the waveforms obtained in step 3 of section 7.5, calculate the conduction and switching
losses of the Diode.
• Using the waveforms obtained in step 4 of section 7.5, calculate the conduction and switching
losses of the MOSFET.
• Using the values of conduction and switching losses of the MOSFET and Diode obtained in
the above steps, estimate the efficiency of the converter. Compare the estimated efficiency
with the efficiency obtained for the buck converter in the ”Buck Converter Experiment”.
What could be the reasons for the difference in values, if any ?
37
38
Experiment 8
Voltage-Mode Control
8.1
Objective
The objective of this experiment, is to design a controller to operate the buck converter in voltage
control mode. For this experiment, a plug-in daughter board will be used to accomplish the control
objective. The small-signal transfer function
vo (s)
d(s)
(d(s) is a small-signal perturbation in the duty
cycle and vo (s) is the corresponding variation in the output voltage) must first be obtained for
the buck converter. The plug-in daughter board is used to implement the voltage-mode control
feedback with the required open-loop gain.
LEM
LEM
V1+
DRIVE
CIRCUIT
V2+
V2+
V1+
Variable
Power
Resistor
Vd
MID POINT
COM
INDUCTOR BOARD
COM
COM
SWITCHED LOAD
DRIVE
CIRCUIT
DIN
ON
PWM TO TOP
MOSFET
USE EXTERNAL
PWM SIGNAL
SWITCHED
LOAD ACTIVE
PWM TO BOT.
MOSFET
USE ONBOARD
PWM SIGNAL
SWITCHED
LOAD OFF
MAGNETICS BOARD
10 Hz
10 % DUTY
DRIVE
SWITCHING
FREQUENCY
ADJUSTMENT
POTENTIOMETER
UNUSED
PWM IC
CONTROL
SELECTION
+12V
0%
100%
-12V
OFF
EXTERNAL
PWM INPUT
EXTERNAL
CONTROL
DUTY CYCLE
POTENTIOMETER
Figure 8.1: Buck Converter Using Power-pole board
39
OPEN
LOOP
8.2
Preparing the Setup and Open-Loop Mode
Construct the buck converter circuit as shown in Fig. 8.1 using the BB magnetics board.
• Connect and turn on the ±12v signal supply and check for green LED.
• Adjust the duty ratio to 50%.
• Adjust the switching frequencyto 100kHz.
• Switch ON the switched load to active position using selector switch bank as shown in Fig.
8.2.
• Adjust the variable load resistance RL to 10Ω.
• Have your circuit checked by your Lab Instructor.
• Apply DC supply voltage Vd to 24V.
Figure 8.2: Selector Switch Position for Switched Load
8.3
Measurements in Open-Loop Operation
Observe and make a copy of the output voltage waveform (V2+). Adjust the timebase to show the
details of the switching transients as the load is switched.
8.4
Preparing the Setup for finding
vo (s)
d(s)
• Turn OFF the supply voltage Vd , the signal supply and remove the jumper J64 (G-5 in Fig.
1.2)
• Switch the switched load OFF as shown in Fig. 8.1.
• Connect the function generator output to J64 (please confirm the polarity of connector).
• Adjust the function generator voltage vi to 200mV peak-peak and 50Hz sinusoidal output.
40
• Keep the variable power resistor at 10Ω and duty ratio at 50%.
• Have your circuit checked bu your Lab Instructor.
• Turn ON the ±12V signal supply and check for green LED.
• Apply Vd =24V.
8.5
Finding Transfer Function
vo (s)
d(s)
• Set the scope to AC coupling to measure the output voltage V 2+ AC ripple.
• Measure the magnitude ratio of V2+ and vi and phase difference between them.
• Repeat the above procedure for different frequencies of vi from 50Hz to 10kHz.
8.6
Type 3 Voltage Controller
Once you get the transfer function or the Bode-plot of the buck converter, you can design a Type-3
voltage controller. The Type-3 voltage control board has the schematic as shown in Fig. 8.3.
Figure 8.3: Voltage Controller Plug-in Board
The values of the resistors and capacitors of the voltage control board are given in Table. 8.1
• Reference value VREF can be set using the duty ratio pot.
• Reference value VREF can’t be set below 10V.
• For the pin details of terminal strip J60, please refer the schematic of the power-pole board.
41
Component
Component Value
R1
100kΩ
R2
20.66kΩ
R3
10.31kΩ
C1
25.19nF
C2
2.5976nF
C3
4.7191nF
Table 8.1: Voltage Control Board Compenent Values
EXTERNAL
CONTROL
OPEN
LOOP
Figure 8.4: Control selection for Voltage-Mode Control plug-in board
8.7
Preparing the Setup for Voltage-Mode Control Operation
• Set the control selection jumpers J2 and J3 (J-5 in Fig. 1.2) as shown in Fig. 8.4.
• Remove the function generator and insert the jumper J64.
• Insert the Voltage-Mode Control plug-in board in the terminal strip 60.
• Keep RL = 10Ω.
• Switch ON the switched load to the active position using the selector switch bank as shown
in Fig. 8.2.
• Turn ON ±12V signal supply and check for green LED.
• Have your circuit checked by your Lab Instructor.
• Set Vd to 24V.
• Use the duty cycle pot RV64 to set V2+ to 12V.
8.8
Measurements in Voltage-Mode Control Operation
Observe and make a copy of the output voltage V 2+.
42
8.9
Lab Report
The lab report should have a brief abstract detailing what has been done in the experiment. The
remaining part of the report should consist of the information asked below along with any discussion
you feel is necessary.
• Construct the bode plot of the small-signal transfer function
vo (s)
d(s)
of the converter from the
results obtained in section 8.5
• Use the K-factor method described in chapter 4 of a “First Course on Power Electronics
and Drives” to design a type 3 voltage mode controller for the buck converter. L = 100µH,
C = 690µF , r = 0.1Ω, fs = 100kHz, Vd = 42V and the duty ratio is set to 50%. The phase
margin of the open-loop transfer function should 60 ◦ at 1kHz.
(Note that these are the same specifications for the voltage-mode control you used in section
8.7).
43
44
Experiment 9
Peak Current Mode Control
9.1
Objective
In this experiment, we will be using a plug-in board to accomplish peak current mode control for
a buck-boost converter. First the aspects of constant frequency peak current mode control will be
explored. Then the plugin board will be used to achieve feedback voltage control of the converter.
The goal is to understand how to design a peak current mode controller with voltage feedback.
LEM
LEM
V1+
DRIVE
CIRCUIT
Vd
V2+
V1+
V2+
MID POINT
INDUCTOR BOARD
COM
COM
COM
SWITCHED LOAD
DRIVE
CIRCUIT
DIN
ON
PWM TO TOP
MOSFET
USE EXTERNAL
PWM SIGNAL
SWITCHED
LOAD ACTIVE
PWM TO BOT.
MOSFET
USE ONBOARD
PWM SIGNAL
SWITCHED
LOAD OFF
MAGNETICS BOARD
10 Hz
10 % DUTY
DRIVE
SWITCHING
FREQUENCY
ADJUSTMENT
POTENTIOMETER
UNUSED
PWM IC
CONTROL
SELECTION
+12V
0%
100%
-12V
OFF
DUTY CYCLE
POTENTIOMETER
EXTERNAL
PWM INPUT
EXTERNAL
CONTROL
Figure 9.1: Current Mode Controller Schematic
45
Variable
Power
Resistor
OPEN
LOOP
9.2
Preparing setup for Open Loop Operation
• Reconstruct the buck-boost converter used in Expt. 3 as in Fig. 9.1.
• Turn on the signal power supply and set the switching frequency to 100 kHz and duty cycle
such that output voltage Vo = 12 V.
• Change the switch positions of the switch bank as shown in Fig. 9.2.
• Set Vd to 20 V and the variable power resistor to 20 Ω .
Figure 9.2: Switch Position for Switched Load
9.2.1
Measurements
• Observe the output voltage V 2+ and inductor current on the oscilloscope.
• Store the waveform.
9.3
9.3.1
Preparing setup for closed loop operation and measurements
Closed Loop Operation Without Slope Compensation
• Setup the control selection as in Fig. 9.3.
EXTERNAL
CONTROL
OPEN
LOOP
Figure 9.3: Switch Position for Closed Loop Operation
46
• Remove shorting link from J61 and insert the Type 2 Controller plug-in board whose circuit is
shown in Fig. 9.4 into the terminal strip J60 (The pin numbers shown in the figure correspond
to pin numbers on the terminal strip). This board will add the voltage feedback to the control.
OUT
IN
VREF
6
11
Figure 9.4: Type 2 Controller
• Set the duty cycle pot to minimum.
• Switch ON the main power supply and set it to 25 V.
• Change the switch positions of the switch bank as shown in Fig. 9.1.
• Switch ON the signal power supply. Ensure that main power supply is ON before signal
power supply is switched ON.
• Observe the PWM and the inductor current waveforms.
• Slowly increase the reference voltage by turning the duty cycle pot clockwise. Observe the
point where the inductor current starts displaying oscillatory behavior. Record the corresponding duty cycle from the scope.
• Plug in the slope compensation jumper on to J61. The slope compensation jumper circuit is
shown in Fig. 9.5. Observe how the inclusion of slope compensation affects the stability of
the converter.
Figure 9.5: Slope Compensation Jumper
47
9.3.2
Closed Loop Operation With Slope Compensation
• Ensure that the plug-in board and the slope compensation jumper are plugged in.
• Set the duty cycle pot to minimum.
• Switch ON the main power supply and set it to 15 V.
• Switch ON the signal power supply.
• Observe the PWM and the inductor current waveforms.
• Slowly increase the reference voltage by turning the duty cycle pot clockwise. Observe the
point where the inductor current starts displaying oscillatory behavior. Record the corresponding duty cycle from the scope.
9.3.3
Dynamic Performance of Closed Loop System
• Ensure that the plug-in board and the slope compensation jumper are plugged in.
• Set the duty cycle pot to minimum.
• Switch on the main power supply and set it to 20 V.
• Switch on the signal power supply.
• Slowly increase the reference voltage to 12 V by turning the duty cycle pot clockwise.
• Observe the output voltage V 2+ and the inductor current on the oscilloscope. Store the
waveform.
9.4
Lab Report
The lab report should have a brief abstract detailing what has been done in the experiment. The
remaining part of the report should consist of the information asked below along with any discussion
you feel is necessary.
• Plot the output voltage Vo and inductor current iL obtained in step 9.2.
• What is the maximum duty ratio stable operation of the converter in step 9.3.1? Plot the
inductor current waveform for stable and unstable operation.
• What is the maximum duty ratio stable operation of the converter in step 9.3.2? Plot the
inductor current waveform for stable and unstable operation.
48
• Explain how slope compensation affects the range of duty cycle obtainable in constant frequency peak current mode control.
• Explain why in step 9.3.1, it is important to switch on the signal power supply after turning
on the main power supply.
• Plot the output voltage Vo waveforms and inductor current in closed loop operations with
output voltage feedback (step 9.3.3).
• Comment on the effect of peak current controller on the operation of converter.
49
APPENDIX
The detailed circuit of the the power-pole is attached. It consists of two sheets.
50
2
1
1, 3
3
2
3
1, 3
1
2
2
10
12 D
PRE
Q 9
CLR
Q 8
4
13
11 CLK
2 D
PRE
Q 5
CLR
Q 6
1
3 CLK